Process for stabilizing or deactivating sludges, precipitates, and residues occurring or used in the manufacture of tetraalkyl leads



Patented Sept. 10, 1946 PROCESS FOR STABILIZING OR DEACTIVAT- ING SLUDGES, PRECIPITATES, AND RESI- DUES OCCURRING R USED IN THE MAN- UFACTURE OF TETRAALKYL LEADS Adrian L. Linch, Wilmington, DeL, assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware N 0 Drawing.

8 Claims. 1

This invention relates to a process for stabilizing or deactivating sludges, precipitates and residues occurring or used in the manufacture of tetraalkyl leads, and which normally tend to pr mote decomposition and ignition of the tetraalkyl leads that may be contained therein.

It is known that alkyl metal compounds in general are quite unstable and decompose readily, particularly in the presence of air or oxygen. It has also been found that these alkyl metal compounds are particularly unstable when adsorbed on materials which present a large surface area per unit Volume such as silica gel, clays, alumina, earths, asbestos, charcoal, and materials of similar structure which materials appear to exert a catalytic effect in the decomposition of these alkyl metal compounds. Even tetraalkyl leads such as tetraethyl lead which is known to be somewhat more stable than some of the other alkyl metal compounds decomposes and often ignites in the presence of oxygen when small amounts are adsorbed on materials that ofier extended surface areas,- particularly when the masses containing the tetraethyl lead are exposed to temperatures somewhat higher than normal atmospheric temperatures. The tendency to oxidize and ignite of course varies with the substance with'which the alkyl metal compound is incorporated,'some materials apparently exerting a greater catalytic efiect than others in promot ing ignition of the alkyl lead compounds.

In the manufacture of tetraalkyl leads, such as tetraethyl lead, tetramethyl lead and the mixed ethyl-methyl lead compounds, sludges are formed from which it is diflicult and, from a practical standpoint, impossible to entirely free from the alkyl lead compounds during the normal steam distillations or decantation operations. There is, therefore, carried through the process very finely divided lead and impurities such as bismuth compounds which, although present in very small amounts, finally are deposited as sludges in the pipes and tanks and other processing equipment and these sludges which contain tetraethyl lead adsorbed therein when exposed to oxygen or air often ignite, thus presenting serious ignition and explosion hazards in the process.

Methods have been advanced for the removal of practically all the sludge forming materials from the tetraethyl lead after its distillation,

Application September 16, 1942, Serial No. 458,579

' such as by controlled blowing with air or oxygen with agitation, preferably under a layer of water; followed by separation of the precipitated sludge, as more particularly described in copending application Ser. No. 393,680. However, even in these cases the sludges which are deposited by the action of the oxidizing agent and which invariably contain tetraethyl lead, tend to ignite when exposed to air thus presenting serious ignition hazards, making it desirable that even these sludges should be deactivated during their formation or afterwards to permit of their removal and disposal in a safe manner.

It is therefore an object of this invention to provide a process for stabilizing sludges, precipitates and residues occurring in the manufacture of tetraalkyl lead compounds whereby the ignition hazard presented by the lead alkyl com pounds in contact with such catalytic surfaces is reducedor completely overcome.

It is a still further object of the invention to render inactive materials which tend to exert a catalytic-effect in the decomposition of tetraalkyl leads in the presence of air thus permitting the safe use of such materials as filter aids in the manufacture of tetraalkyl lead.'

I have found that the sludges, precipitates and residues occurring or involved in the production of tetraalkyl leads, which offer large surface areas per unit volume and which normally tend to exert'a catalytic efiect and cause decomposition and ignition of the tetraalkyl lead which may be contained therein, can be rendered inactive conveniently and economically by washing or otherwise treating them with solutions or dispersions of polyfunctional phenols. These stabilizing agents appear to be preferentially absorbed by the active materials which appear to retain their capacity to absorb the alkyl lead although they are no longer effective to induce ignition of the tetraalkyl lead absorbed therein.

By the terms sludges, precipitates and residues I include those filter aids which may be employed in the production of the tetraalkyl leads and which ofier a large surface area per unit volume and are known to accelerate decomposition of the tetraalkyl leads on exposure to air or oxygen such as clays, silica, earths, charcoal, etc. These filter aids are rendered inactive by treating them with polyfunctional phenols either before or hydroxy (-OI-I), alkoxy (OR), carboxy (--COOH) aldehyde ketone R Lao) nitro (-NO2), nitroso (-NO), hydroxy benzyl (-CH2.CsI-I4.OH) phenolic ester and long chain aliphatic radicals of at least 4 carbon atoms. The derivatives of the above compounds which produce such polyfunctional compounds by hydrolysis, for example, picryl chloride, hydroquinone diacetates, etc., are also effective. Further, the diketones, formed from the polyfunctional phenols by simple oxidation or tautomerization such as chloranil, benzoquinone; quinhydrone; alpha nitroso beta naphthol; para-nitroso phenol, etc., are effective deactivating agents.

The polyfunctional phenol deactivators are preferably used as aqueous solutions which contain the deactivating agent in an amount equivalent to approximately one-third of the dry weight of the material to be stabilized. The

amount of deactivator employed may of course be varied over a wide range with equally good results. By employing the stabilizer in an amount ranging from 0.05% to more than 100% of the dry weight of the active material satisfactory re-- sult have been obtained. The stabilizing effect may be obtained in some cases by using even smaller amounts of the deactivating agent, although a sufficient amount should always be used to insure complete deactivation of the active material. The use of excessively large quantities over that actually required to deactivate the active materials merely contributes unnecessarily to the cost of the process and serves no useful purpose.

The deactivating agent is preferably employed in a solution of a concentration of from 1 to 5% although lower or higher concentrations may be used. It is of course advantageous to employ a sufficient amount of solution to insure complete contact of all the material to be deactivated. To prevent the use of unnecessary large amounts of the deactivating polyfunctional phenol, it will usually be found desirable to use a relatively large Volume of solution of a concentration of less than 5%. Where there is an advantage of employing a lesser volume of solution the concentration may of course be increased.

An important use of the present invention in the commercial manufacture of tetraethyl lead is to deactivate the sludges which are precipitated and removed from the crude tetraethyl lead in the purification step. A method of precipitatin and removing these sludges by treating the crude tetraethyl lead with oxidizing agents such as with air or oxygen is more particularly disclosed in copending application Ser. No. 393,680. The precipitated sludges from this process collect in the aqueous layer from which the purified tetraethyl lead is separated by decantation. Although dispersed in the Water layer the sludge retains sufiicient tetraalkyl lead absorbed therein to ignite on contact with oxygen or air, particularly at slightly elevated temperatures. In order to permit the safe handling and disposition of these sludges it has been found desirable to deactivate them before they are removed from the system. This can be done conveniently by adding a quantity of one of the deactivating agents to the aqueous sludge dispersion and then agitating the mass to assure complete contact of all the sludge with the deactivating material, or an aqueous solution of the deactivating agent may be used to cover the tetraalkyl lead during the accelerated sludge precipitation treatment so that the sludge is deactivated as fast as it is formed.

The deactivating material may be employed in an aqueous solution or suspension or in other solvents.

Where the sludges or precipitates settle out in the pipe lines or other processing equipment during the manufacture or purification of the tetraalkyl leads they may be deactivated, to insure safety in their removal or during repair of the equipment, by pumping a solution of one of the deactivating materials through the apparatus for a sufficient period of time to insure complete contact with all the sludge to be deactivated, which is usually accomplished in from 15 to minutes.

The filter aids may be washed with a solution of the deactivating agent prior to their use in the process. They may be employed either before or after drying, for it has been found that they do not again become active even after being dried, or by being washed by the solutions that are filtered therethrough.

In view of the fact that these polyfunctional phenols are in the main volatile with steam they can be added to the crude tetraalkyl lead mass at the time of steam distillation so that they are carried over with the tetraalkyl lead and continually effect the stabilization of any residues that may occur in the process.

aqueous solution of one of the deactivators disclosed may be used to cover the crude tetraalkyl lead. Any sludge which precipitates at the surface of the lead alkyl on standing is stabilized by contact with the aqueous layer. If desired, all of the precipitated sludge may be brought into the aqueous layer by suitable agitation since the stabilized sludge particles readily disperse in the water layer. In this way the sludge may be deactivated as soon as it is formed.

Stabilization of sludge formed in crude tetraethyl lead on standing is also accomplished without the use of an aqueous layer over the material. Some of the deactivating agents mentioned are soluble in tetraethyl lead and may be dissolved directly in the crude tetraethyl lead. Any sludge which precipitates while the tetraethyl lead is in storage is immediately rendered safe by the reagent.

The following examples are given to illustrate the invention. The parts used are by weight.

EXAMPLE 1 Approximately 25,000 part of tetraethyllea'd were processed in a washer to precipitate the sludge forming impurities by the method described in the co-pending application, Serial Number 393,680. The-precipitated sludge which, by laboratory analysis of a small sample of the tetraethyl lead, had been calculated to weigh 30 parts, was collected in 2,500 parts of water. The purified tetraethyl lead was then decanted from the water layer. Approximately 25 parts of hydroquinone were added to the aqueous phase producing a solution of about 1.0% hydroquinone. The mixture was agitated for minutes and filthe clear tetraethyl lead was decanted from the water layer after the filtration was complete. A sample of the sludge retained on the filter was tested for ignition activity as previously described, and was found to be inactive. Sludge obtained using the same crude tetraethyl lead and the same process, exceptthat potassium alizarinate was omitted, ignited the tetraethyl lead which it retained when placed on the steam bath.

Although I use potassium alizarinate in this example, the same procedure may be employed with the other deactivating agents mentioned. It is also to be understood that'the quantities and concentrations given are not to be construed as terecL l5 limits to the invention for they may be varied A small portion of thefilter cake was then wldelr wtthout modlfytng the resultstested for ignition activity by placing it on a P? m the preceilmg examples]: used filter paper, wetting the cake with a smauquan; stabilizing agent WhlCh are soluble in neutral tity of tetraethyl lead and heating on a, steam .aquemls 591111310115 deactwatmg that are bath 95-100 0.). No signs of ignition or char- 11150121318 m miutral 50mm? m be ring of the filter paper were noted even after 24 efieqtlvely apphed from. Suitable Solutlons! Such hours on the Steam bath. as d lute sodium hydroxide, or from organic sol- A sample of the same sludge which was taken t I found that dlsPerslfnsi t before the hydroqumone was added to the water sions or solutions of the deactivating agent in layer was tested for activity as outlined above. 25 Solvents Water may be efiectlvply Ignition occurred shortly after the initial sample n Water 15 used as the sqlvent or dlspfersmg was placed on the Steam bath medium, the method of applying the deactivator In regular plant application of this method of g i gfi g f f l f l sgldges g g we pie asse o in xampes r. sludge deactlvatlon not always be con However, when solvents other than water are venient to run a laboratory analysi in order to determine the amount of sludge to be expected. I have found that under usual conditions the quantity of sludge formed per 1,000 parts of tetraethyl lead seldom exceeds 2 parts and this figure may be used as a basis for calculating the quantity of deactivator needed. Since tetraethyl lead manufactured in various plants may vary in sludge formation, depending on the quality of raw materials employed for any particular plant the used, the aqueous layer containing the sludge may be filtered off, and the filter cake then agitated with the solution containing the deactivating agent for a period of from 15 to 30 minutes in a suitable receptacle, or the solvent solution may be added directly to the aqueous sludge suspension. Results obtained on agitating 10 parts of an active sludge with 50 parts of a solution of representative polyfunctional phenols in various quantity will be relatively constant the amount of solvents are listed in the table below.

Table I I concem Steam bath stability Compound tration, Solvent Initial percent After 24 hours After 72 hours Hydroquinone 5 5% N21 00:.-- No decomposition--. N0 decomposition-.. No decomposition. 8-hydroxy quinoline 1 1% NaO C Hg..- do d0 Do. Alpha-nitroso beta-naph ol 1 Ethyl alcohol. do Do. Pyrogallol 2 Water Do. Sodium picrate 2 .do D0. Chloranil 2 Ethyl alcohol. Do. 4,4-dihydroxy diphenyl methane. 2 Cello Do. Catechol-mono-ethyl ether 2 Do. 5-methyl-2-liydroxy acetophenona 2 Do. 4-Iaur0yl resorcinol 2 Do. l-hydtoxy--napthoxy acetic acid. 2 D0. Para-stearylphenol 2 Do. Leuco-2,2'-dimethoxy dibenzan 1 Do. Picryl chloride 1 Do. Salicylal aldoxime- 1 Ethyl alcohoL .do Do. No deactivator (control) Water Ignited... Do.

deactivator required for that plant per unit weight to As previously stated the invention may be emof tetraethyl lead may be readily determined.

EXAMPLE 2 all ployed to stabilize active filter aids which are to be used in tetraalkyl lead filtration. These materials may be washed in a solution of one of the deactivators and rendered suitable for tetraalkyl lead filtration. The following filter aids as well as a number of other materials of similar structure were wet with tetraethyl lead and placed on a steam bath as described in Example 1 above. All were found to initiate the ignition of tetraethyl lead. Ten parts of each of these materials were then agitated for several hours with parts of the solution of various polyfunctional phenols of the concentrations given in Table 2. After the agitation period, the solutions were filtered and 75 portions of the filter cakes were wet with tetra- 7 ethyl lead and placed on a steam bath. Results of the tests are given below:

by hydrolysis of Bi(NOs):l.

Bismuth oxide (prepared by hydrolysis of BKNOg);

2% d-lauroyl resorcinol No decompoin ethyl alcohol.

Activated Alumina None Ignited.

Do 2% guaiacol in ethyl No decompo' alcohol. sition.

Decolorizing charcoal None Ignited.

Do 2% picric acid in 2% No decompo- NaOH. sition.

EXAMPLE 3 Approximately 2,000 parts of crude tetraethyl lead were placed in a suitable tank or washer, and an approximately equal weight of water was added to the tetraethyl lead. Some 40 parts of NaOI-I and 40 parts of guaiacol were then added to the water layer, and the sludge was precipitated and removed from the tetraethyl lead by blowing with air as more particularly disclosed in the copending application, Serial Number 393,680. After this operation was complete, the tetraethyl lead was removed by decantation, and the aqueous layer containing the sludge was filtered. A portion of the filter cake was tested on the steam bath as described in Example 1. No decomposition or ignition of the tetraethyl lead was noted.

EXAMPLE 4 As previously stated, sludges found in tetraethyl lead are also found in other lead alkyls which are manufactured from commercial lead. An example of these alkyls is the mixed tetramethyl-ethyl compounds of lead, formed when a mixture of methyl chloride and ethyl chloride are reacted with lead sodium alloy. All examples in which tetraethyl lead is specified are equally workable with these mixed lead alkyls.

Approximately 8,000 parts of crude mixed tetramethyl-ethyl lead compounds (tetramethyl lead, trimethyl ethyl lead, dimethyl diethyl lead, methyl triethyl lead and tetraethyl lead) were placed in a suitable tank or washer, and 2,000 parts of water containing parts of sodium alizarinate were added. The contents of the tank were aerated and agitated for two hours as disclosed in the copending application, Serial Number 393,680. After a settling period of a few minutes, the clear mixed lead alkyls were decanted from th aqueous layer and the aqueous mixture was filtered. A portion of the filter cake was tested on the steam bath as described in Example 1 except that the filter cake (sludge) was wet with mixed lead alkyl compounds rather than with tetraethyl lead. No decomposition or ignition of the lead alkyls was noted. A similar experiment was carried out in which no sodium alizarinate was placed in the water layer. This sludge ignited the mixed alkyls when the steam bath stability test was made.

In testing the activity of the sludges before or after treatment with the deactivating agents it will be noted that tetraethyl or other alkyl lead was added to the residues. This was to make sure there was sufficient tetraalkyl lead present to ignite under the conditions employed, if the sludge was not fully inactivated, for in some instances, it is possible that the amount of alkyl lead may be reduced to such a small amount that ignition might not be noted. While the elimination of the alkyl lead from the residues to such an extent does not ordinarily take place, the tests were made under conditions favoring ignition provided the sludge or filter aid was active.

This invention makes possible the deactivation of theignitable sludges and residues occurring in the manufacture or tetraalkyl lead compounds and is of particular value, in eliminating fire and explosion hazards involved in the removal and disposal of such sludges from the process and in overcoming the potential fire hazard arising from the collection of such sludges and precipitates which accumulate in various places in the processing equipment and which when exposed to air often ignite with considerable damage. The invention also permits the use of filter aids which unless rendered inactive tend to cause ignition of any absorbed tetraethyl lead when they are exposed to the air. Any other absorbent materials which for any reason may become saturated with tetraethyl lead in or about the plant in which it is being manufactured may be rendered inactive by washing or otherwise treating with stabilizers of the type described so that potential fire hazards may be removed as far as possible. Lagging on pipe which due to leaks may become saturated with tetraethyl lead and which have been known to cause its ignition can be inactivated by treating such lagging with the deactivating agents.

1 claim:

The process for inhibiting the spontaneous ignition of tetraalkyl lead compounds adsorbed on sludges which are precipitated from crude tetraalkyl lead compounds and which sludges normally tend to cause spontaneous ignition of the tetraalkyl lead compounds adsorbed thereon'when exposed to oxygen, which comprises incorporating with such sludges a phenol containing at least one substituent of the group consisting of hydroxy, alkoxy, carboxy, aldehyde, ketone, nitro, nitroso and ester groups attached to ring carbon atoms and which otherwise consists of carbon, hydrogen and oxygen.

2. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises incorporating with such sludges a phenol containing at least one substituent of the group consisting of hydroxy, alkoxy, carboxy, aldehyde, ketone, nitro, nitroso and ester groups attached to ring carbon atoms and which otherwise consists of carbon, hydrogen and oxygen.

3. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises washing such sludges with a solution of a phenol containing at least one substituent of the group consisting of hydroxy, alkoxy, carboxy, aldehyde,

ketone, nitro, nitroso and ester groups attached to ring carbon atoms and which otherwise consists of carbon, hydrogen and oxygen,

4. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises washing such sludges with an aqueous solution of a phenol containing at least one substituent of the group consisting of hydroxy, alkoxy, carboxy, aldehyde, ketone, nitro, nitroso and ester groups attached to ring carbon atoms and which otherwise consists of carbon, hydrogen and oxygen.

5. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spon taneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises incorporating with such sludges hydroquinone in an amount equivalent to at least 0.05 per cent of the dry weight of the sludge.

6. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises incorporating with such sludges guaiacol in an amount equivalent to at least 0.05 per cent of the dry weight of the sludge.

7. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises incorporating with such sludges picric acid in an amount equivalent to at least 0.05 per cent of the dry Weight of the sludge.

8. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises washing such sludges with an aqueous solution of hydroquinone.

ADRIAN L. LIN CH. 

